COLUMBUS, Ohio (AP) — A bill imposing one of the most stringent abortion restrictions in the nation was signed into law in Ohio on Thursday, banning abortions after a detectable heartbeat in a long-sought victory for abortion opponents that drew an immediate constitutional challenge.

In signing the heartbeat bill, Republican Gov. Mike DeWine broke with his predecessor, Republican John Kasich, who had vetoed the measure twice on grounds that it was unconstitutional.

But DeWine defended Ohio Republicans’ decision to push the boundaries of the law, because “it is the right thing to do.”

“Taking this action really is a kind of a time-honored tradition, the constitutional tradition of making a good faith argument for modification or reversal of existing legal precedents,” he said. “So that is what this is.”

He said it’s the government’s job to protect the vulnerable. The bill outlaws abortions once a fetal heartbeat is detected, which doctors say can be as early as five weeks into pregnancy, before many women know they are pregnant.

Ohio’s closely divided politics had slowed the progress of the bill as it has caught momentum elsewhere , forcing years of debate in the state where the movement originated. Of five previous states that have passed heartbeat bills, three have seen their laws struck down or blocked by the courts, another faces a legal injunction and the fifth is awaiting governor’s action.

Even before the bill was signed, the ACLU of Ohio said it was preparing a constitutional challenge to the law on behalf of Pre-Term Cleveland and three other Ohio abortion clinics.

The legal challenge is what the bill’s backers have always wanted. They hope to provoke a legal challenge with the potential to overturn the U.S. Supreme Court’s 1973 Roe v. Wade ruling that legalized abortion up until viability, usually at 22 to 24 weeks.

“The heartbeat bill is the next incremental step in our strategy to overturn Roe v. Wade,” said Ohio Right to Life President Mike Gonidakis. “While other states embrace radical legislation to legalize abortion on demand through the ninth month of pregnancy, Ohio has drawn a line and continues to advance protections for unborn babies.”

Kellie Copeland, director of NARAL Pro-Choice Ohio, said lawmakers and the governor have plunged the state into “a dystopian nightmare where people are forced to continue pregnancies regardless of the harm that may come to them or their family.”

The law makes no exceptions for pregnancies resulting from rape or incest.

EMILY’s List, a national group that supports candidates who favor abortion rights, also decried the Ohio bill, as did the Democratic National Committee.

DNC CEO Seema Nanda called it “the latest example of how the Trump administration’s extremist, anti-women policies have emboldened legislators across the country to attack women’s access to health care.”

DeWine said his administration is committed to supporting pregnant women.

“I just want to make it very, very clear, our concern is not just for the unborn, our concern is for all individuals who need protection,” he said. “It is our duty, I believe, and an essential function of government, to protect those who cannot protect themselves.”